<!DOCTYPE html>
<html lang="en">

    <head>
        <meta charset="UTF-8">
        <title>微信登录</title>
    </head>

    <body>
        <script>
            var GWC = {
                version: '1.1.1',
                urlParams: {},
                appendParams: function(url, params) {
                    if (params) {
                        var baseWithSearch = url.split('#')[0];
                        var hash = url.split('#')[1];
                        for (var key in params) {
                            var attrValue = params[key];
                            if (attrValue !== undefined) {
                                var newParam = key + "=" + attrValue;
                                if (baseWithSearch.indexOf('?') > 0) {
                                    var oldParamReg = new RegExp('^' + key + '=[-%.!~*\'\(\)\\w]*', 'g');
                                    if (oldParamReg.test(baseWithSearch)) {
                                        baseWithSearch = baseWithSearch.replace(oldParamReg, newParam);
                                    } else {
                                        baseWithSearch += "&" + newParam;
                                    }
                                } else {
                                    baseWithSearch += "?" + newParam;
                                }
                            }
                        }

                        if (hash) {
                            url = baseWithSearch + '#' + hash;
                        } else {
                            url = baseWithSearch;
                        }
                    }
                    return url;
                },
                getUrlParams: function() {
                    var pairs = location.search.substring(1).split('&');
                    for (var i = 0; i < pairs.length; i++) {
                        var pos = pairs[i].indexOf('=');
                        if (pos === -1) {
                            continue;
                        }
                        GWC.urlParams[pairs[i].substring(0, pos)] = decodeURIComponent(pairs[i].substring(pos + 1));
                    }
                },
                doRedirect: function() {
                    var code = GWC.urlParams['code'];
                    var appId = GWC.urlParams['appid'];
                    var scope = GWC.urlParams['scope'] || 'snsapi_base';
                    var state = GWC.urlParams['state'];
                    var redirectUri;

                    if (!code) {
                        //第一步，没有拿到code，跳转至微信授权页面获取code
                        redirectUri = GWC.appendParams('https://open.weixin.qq.com/connect/oauth2/authorize#wechat_redirect', {
                            'appid': appId,
                            'redirect_uri': encodeURIComponent(location.href),
                            'response_type': 'code',
                            'scope': scope,
                            'state': state,
                        });
                    } else {
                        //第二步，从微信授权页面跳转回来，已经获取到了code，再次跳转到实际所需页面
                        redirectUri = GWC.appendParams(GWC.urlParams['redirect_uri'], {
                            'code': code,
                            'state': state
                        });
                    }

                    location.href = redirectUri;
                }
            };

            GWC.getUrlParams();
            GWC.doRedirect();
        </script>
    </body>

</html>
